Electrical signal generators are used in a variety of medical applications. Examples include electrosurgery, tissue ablation, tissue perforation, neural stimulation, and neural lesioning. Neural lesion procedures using electrical current with a high frequency wave, typically in the radiofrequency (RF) spectrum, have been in use since the early 1950s. Among a variety of therapeutic purposes, the application of RF in the nervous system is commonly used in the interventional treatment of pain. The principle of this application is to intervene in the transmission of pain signals by altering a function of a nerve structure. This is accomplished by controlled generation of heat, or, non-thermal delivery of RF current using an electrode connected to the generator. Modern RF electrodes not only deliver current but also include temperature sensors that feedback information to the controller. And thus, in this situation the energy application tool is interchangeably referred to as a RF electrode and RF probe. One of the major advantages of using electrical current for interventional pain management is that by applying appropriate frequencies, the current can be used to stimulate nerves adjacent the electrode to differentiate pain fibers from other neural fibers and ensure the correct placement of the electrode prior to intervention.
Currently, in the field of interventional treatment of chronic pain the specialist commonly uses three modes of RF treatment including standard RF, pulsed RF and intradiscal lesioning. Each of these treatment modes is based on the application of continuous or pulsed radiofrequency electrical current to tissue or to an application tool. For some procedures, prior to applying radiofrequency energy, the target site is stimulated using stimulation modes to ensure correct placement of the RF delivery probe.
RF Lesioning Devices—Probes and Cannula
Probes are medical devices that are designed to act as patient/energy interfaces for radiofrequency generator systems. The RF energy applied is usually a 400 to 900 kHz waveform that can be used for a variety of purposes. In most radiofrequency generators, the 460-500 kHz waveform is delivered to the body using a probe and cannula system. A cannula is a hypodermic needle with an insulated shaft and a bare metal tip called an active tip. It is called an active tip because once the probe is inserted into the cannula and the RF is activated, the tip becomes the energy delivery mechanism. The electrical circuit required to deliver current and voltage is provided by a return electrode pad that is placed on a flat body part of the patient, such as his thigh. When the RF energy is activated at the machine, RF is delivered to the cells surrounding the active tip surface area. With energy application, the cells move faster and generate heat. As this heat increases, it is detected by the temperature measurement device that is located in the probe.
Therefore, the mono-polar probe serves two major functions, it is used for RF energy delivery to the cannula and temperature monitoring through a thermocouple effect. In some cases, the probes are not truly heating devices (i.e. resistive elements), but rather passive energy delivery systems.
Intradiscal Lesioning Devices Probes
Historically, intradiscal devices work the principle described above or on a different principle. Still using RF energy (for example, at 460 kHz) these bi-polar probes are designed to be heating elements. There is a resistive element in the probe that generates heat. When this probe is placed in the body it radiates heat to the tissue that surrounds it. There is no need for a return electrode, but there is a need to measure the temperature and provide that information to the generator for a temperature control function.
Therefore, the bi-polar probe serves two major functions. It is used for delivery of heat energy to the tissue in the disc and for temperature monitoring through a temperature sensor.
A limitation of conventional signal generators is that they are built with switches and controls hardwired in a dedicated manner for the specific generator. The components are therefore securely connected to each other for a specific function with limited reliance on the operation of a central processing unit. This limits the ease of use and adaptability of the signal generator.
For example, at the time of purchasing new medical probes for a new technique, it is common to acquire, at the same time, a dedicated electrical signal generator. Consequently, there is a significant cost associated with purchasing, storing and maintaining dedicated electrical signal generators for a large variety of medical probes. Upgrading a hardwired electrical signal generator to accommodate a new medical probe is costly, if possible at all. It is very difficult to change the functions of the machine without changing the actual physical parts and without adding user input controls such as buttons, switches and dials. In the Pain Management field, for example, this is costly and inefficient because there are a growing number of procedures being developed for the treatment of pain. Furthermore, the addition of the new technique decreases the ease of use as additional user input controls or components are added to the existing system.
Another example of this limitation is that there is also a significant cost related to training personnel, both doctors and nurses, in the use of such signal generators. Especially since this training must be done for each new signal generator. Each signal generator has its own proprietary configuration and requirements for use. The nurse or doctor must set switches and controls to desired settings prior to use.
Currently, the generic signal generators are very complex to use and require extensive training of personnel who operate them. The flow of operations is not intuitive and there is no support for the user for troubleshooting. Furthermore, excessive control buttons and switches that are not always needed for every procedure complicate the user interface. The complexity and lack of operational information makes the use of the current generators time consuming, frustrating and costly for the physicians because of increased training required.